1. Field
The present disclosure relates to a high-pressure extraction apparatus, and more particularly to a continuous supercritical extraction apparatus.
2. Related Art
Supercritical fluid extraction technologies generally include steps of placing a substance-to-be-extracted in a chamber, filling the chamber with a medium until the medium reach the supercritical state, and then extracting the substance by the medium. The medium at the supercritical state exhibits high diffusibility as gas phase and strong solvent power as liquid phase. Generally, the method for enabling the medium to reach the supercritical state is to fill and pressurize the chamber with the medium, so as to increase the pressure in the chamber, till the pressure reaches a supercritical point of the medium.
Currently, a supercritical extraction apparatus is usually operated by batch. After each batch of extraction, the chamber is depressurized to the atmospheric pressure first, an extraction residue is discharged, and then a new batch of substance-to-be-extracted is fed into the chamber. According to the procedure, in each batch operation, pressurization and depressurization need to be performed. In addition, for a large scale chamber at the depressurization process, oil pressure device is needed to open a cover of the chamber. Those operations are very time-consuming. Further, the fed medium is exhausted and wasted as well as the pressure loss occurs during the depressurization. Upon this kind of supercritical extraction apparatus, a larger scale chamber will make the aforementioned problems worse.
In addition, some technologies propose continuous supercritical extraction technologies, for example, in U.S. Pat. No. 5,939,571 and Japanese Patent No. JP6233901A. U.S. Pat. No. 5,939,571 describes a device for the production of oils by pressing and extracting a raw material containing oleiferous or extractable substances in the presence of a liquid or supercritical extraction agent. The device includes an inlet for said raw material, a substantially cylindrical pressing body having outlets for oils and being connected to said inlet, and a press screw movably provided in said cylindrical pressing body whereby said raw material is transported from said inlet into said pressing body and therefrom to a discharge outlet while being pressed. In addition, the pressing body is proof-sealed against its surroundings by a jacket and the press screw and/or the pressing body include outlets wherethrough a liquid extraction agent may be introduced into said raw material present in said pressing body. At the outlet of said pressing body, a pipe permitting degassing of the press cake discharged from the press by applying a vacuum, thus removing the solvent from it, may be provided.
In Japanese Patent No. JP6233901A, the continuous feeding of a high pressure fluid is achieved through reciprocation of a hard bead in a check valve.
Additionally, a substance for extraction is usually a dry substance, a substance after drying, or a substance with a large particle size according to the present supercritical extraction technology. The reason is that a wet substance for extraction would causes liquid seal (blocking and/or bypassing) of the medium during supercritical extraction. The liquid seal phenomenon results in poor extraction. Chinese Patent No. CN1448383A, US Patent Publication No. US20050266132A1, and US Patent Publication No. US20080146851A1 disclose technologies all concerning extraction performed on dry algae. As for extraction performed on wet algae, reference can be made to the paper about extraction performed on pythium irregulare with supercritical carbon dioxide by Walker et al. The paper suggests that when the moisture content of a substance for extraction is 10 wt % (weight percentage), the extraction yield is 60%, and when the moisture content of the substance for extraction is 30 wt %, the extraction yield is decreased to 32%. The result indicates that, the supercritical extraction is difficult to be applied to the extraction of wet algae.